1. Field of the invention
This invention relates to a semiconductor laser array apparatus in which the oscillation threshold current level of the semiconductor laser devices of the non-laser oscillation-operating areas is set to be so high that laser oscillation of the semiconductor laser devices of the non-laser oscillation-operating areas can be suppressed and laser oscillation in the laser oscillation-operating area alone can be achieved, resulting in a stabilized near-field pattern.
2. Description of the prior art
In recent years, high-output power semi-conductor laser array apparatuses in which a plurality of semiconductor laser devices are disposed with a certain gap therebetween on a single substrate have been developed. These semiconductor laser array apparatuses are produced by liquid phase epitaxy by the use of substrates with grooves so that light beams and current can be regulated.
FIG. 4 shows a conventional synchronous phase-type semiconductor laser array apparatus, which is produced as follows: On a p-GaAs substrate 1, an n-Ga.sub.0.9 Al.sub.0.1 As current blocking layer 2, and an n-GaAs current blocking layer 3 are successively formed by liquid phase epitaxy. Then, a plurality of grooves 4 are formed in a parallel manner, corresponding to the laser oscillation-operating area 5, in such a way that they reach the GaAs substrate 1 through the current blocking layers 2 and 3. Then, on the n-GaAs current blocking layer 3, a p-Ga.sub.1-x Al.sub.x As cladding layer 6, a p-(or n-)Ga.sub.1-y Al.sub.y As active layer 7, an n-Ga.sub.1-x Al.sub.x As cladding layer 8, and an n-GaAs cap layer 9 are successively formed by liquid phase epitaxy. A p-side electrode 11 and n-side electrode 12 are formed on the bottom face of the GaAs substrate 1 and the top surface of the n-GaAs cap layer 9, respectively. Current is injected into the active layer 7 through the grooves 4, resulting in optical waveguides within the active layer 7 that correspond to the grooves 4. The area including each of the grooves 4 constitutes an individual semiconductor laser device, and light beams that are oscillated by these laser devices are coupled therebetween, resulting in high-output power laser beams. However, in the laser oscillation-operating area 5 in which the grooves 4 are disposed, the top surface of the p-Ga.sub.1-x Al.sub.x As cladding layer 6 is bent, resulting in a bend of the active layer 7 formed thereon. Thus, the semiconductor laser devices become unsymmetrical, which makes weak the optical coupling between the adjacent semiconductor laser devices so that the semiconductor laser devices individually oscillate laser beams. That is, it is difficult for all of the semiconductor laser devices to attain uniform oscillation in the state that they are optically coupled therebetween.
To overcome this problem, semiconductor laser array apparatus shown in FIGS. 5 and 6 have been proposed. The semiconductor laser array apparatus of FIG. 5 has a plurality of grooves 4 with a certain pitch on the entire surface of a p-GaAs substrate 1 so that a uniform active layer 7 can be obtained. Moreover, this apparatus has an n-GaAs current blocking layer 26 between the p-GaAs substrate 1 and the n-Ga.sub.0.9 Al.sub.0.1 As current blocking layer 2 at the outside of the laser oscillation-operating area 5 so that current cannot be injected into the portions of the active layer 7 at the outside of the laser oscillation-operating area 5. The semiconductor laser array apparatus of FIG. 6 also has a plurality of grooves 4 with a certain pitch on the entire surface of the p-GaAs substrate 1. This apparatus has a proton-injected region 10 in both the n-GaAs cap layer 9 and the n-Ga.sub.1-x Al.sub.x As cladding layer 8 at the outside of the laser oscillation-operating area 5 so that the injection of current into the active layer 7 can be prevented.
However, these apparatus shown in FIGS. 5 and 6 have the grooves 4 in the non-laser oscillation-operating areas outside of the laser oscillation-operating area 5, and accordingly there is a possibility that optical coupling can be attained between the adjacent semiconductor laser devices in the non-laser oscillation-operating areas. Thus, when current injected into the active layer 7, leaks in the lateral direction, the semiconductor laser devices of the non-laser oscillation-operating areas attain laser oscillation and/or attain optical coupling therebetween, resulting in a bad influence on the oscillation mode of the laser oscillation-operating area 5.